1. Field of the Invention
This invention relates to an information processing apparatus which two-dimensionally scans a medium by a probe and effects recording and reproduction by the physical interaction of the medium and the probe, or to a scanning type tunnel electronic microscope (STM). The invention, more particularly, relates to an STM and a compact and high-density information processing apparatus to which the principle of the STM is applied.
2. Related Background Art
In recent years, there has been developed a scanning type tunnel microscope (hereinafter referred to as STM) which can directly observe the electron structure of the surfaces of substances and the vicinity of the surfaces (G. Binnig et al., Helvetica Physica Acta. 55. 726 (1982)), and it has become possible to observe real spatial images at a high resolving power irrespective of single crystal or noncrystal and moreover, this STM has the advantage that measurement can be accomplished with low electric power substantially without imparting damage by electric current to sample substances, and further it operates not only in super-light vacuum but also in the atmosphere and in solution and can be applied to various materials. Therefore, its wide application is expected.
The STM utilizes the phenomenon that when a voltage is applied to between a metallic probe and an electrically conductive sample and the probe is brought to a distance of about 1 nm with respect to the sample, a tunnel current is created. Recently, as disclosed, for example, in Japanese Laid-Open Patent Applications Nos. 63-161552 and 63-161553, there have been made numerous proposals to utilize the principle of this STM to construct an information processing apparatus directed chiefly to high-density recording and reproduction. That is, it is said that if use is made of a method of imparting physical deformation onto a recording medium corresponding to a sample by a probe electrode corresponding to the probe of the STM, or varying the electron state of the surface of the medium to thereby record information, and reproducing the information of a recording bit by a tunnel current flowing between the probe electrode and the recording medium, large-scale information can be recorded and reproduced at high density of the molecular or atomic order.
It has recently been reported that in the above-described recording method, to impart physical deformation onto the recording medium, a hole can be formed not only by urging a pointed recording probe against the recording medium to thereby dent the latter, but also by applying a pulse voltage onto a recording medium such as graphite. That is, the probe electrode is brought close to the surface of the recording medium, and then applying a voltage of 3-8 V with a pulse width of 1-100 .mu.s to between the two, a hole having a diameter of the order of 40 angstroms can be formed, and such a hole is readily usable as a recording bit. On the other hand, to vary the electron state to thereby effect recording, there is known a method of applying a voltage to between a recording medium and a ground electrode and a probe electrode to thereby vary the electrical resistance characteristic of a minute portion, and attention has been paid to this method because of the ease of erasing and rewriting.
As the recording medium, use is made of a thin film layer of a material such as a chalcogenide or an organic compound of the .pi. electron family which exhibits a switching characteristic having a memory property in a voltage-current characteristic, for example, a cumulative film of an appropriate organic substance made on a ground electrode by Langmuir-Blodgett's technique (hereinafter referred to as LB technique).
The probe electrode is usually, for example, a needle tip of tungsten, Pt-Ir, Pt or the like mechanically polished and thereafter polished by an electric field and attached to a piezo-electric element, and displacement-controlled by an applied voltage. As a method of making a flexible portion for moving the probe electrode, there is, for example, a working technique making a minute structure on a substrate (K. E. Peterson, "Silicon as Mechanical Material", Proceedings of the IEEE, 70, Vol. 420 p, 1982) by using a semiconductor processing technique. Thereby, it has become possible to form a hole portion 30 in a single crystal silicon substrate 21 shown, for example, in FIG. 9 of the accompanying drawings, to provide a tongue-like finely moving mechanism 2 on the silicon substrate 21 by cantilever support, and mount a probe electrode 1 on the front end thereof.
The tongue-like portion 2 is comprised of a layer-like piezo-electric element and electrodes, and by applying voltage between the electrodes, the probe electrode is varied in a direction perpendicular to the plane of the single crystal silicon substrate 21 (the direction of the Z axis). As regards displacement in XY direction, relative movement is effected by the silicon substrate or a medium opposed thereto being installed on a stage capable of scanning. Of course, at this time, there can be realized a memory device provided with a converter array having a number of tongue-like portions 2 arranged thereon. Besides the tongue-like portion 2 of such cantilever structure, a tongue-like portion of a bridge-like twin beam structure is also known.
It is very important in achieving the compactness, the great capacity and the high speed of an information processing apparatus to form a probe having a finely moving mechanism by minute working. On the other hand, however, it results in crosstalk and deterioration of S/N ratio because a signal system for driving and a signal system for recording and reproduction come very close to each other.